The present invvention relates to laboratory test equipment for analyzing liquid samples, such as blood specimens, and more particularly to automated equipment for quickly diluting liquid samples in accurate proportions with a volume of diluent which typically is substantially greater than the sample volume.
In many laboratory procedures, it is necessary to repeatedly dilute very small volumes of sample material. Normally the sample material, such as blood serum, is picked up in a relatively small volume sample syringe while the diluent is picked up by a separate diluent syringe having a relatively large volume. For example, a diluent syringe of 1000 microliters might be used with a 25 microliter sample syringe.
To increase the speed and ease of sample preparation, diluting systems have been developed which automatically operate these separate diluent and sample syringes. Such known systems automatically zero each of the two separate syringes, withdraw the syringe plungers from the syringe barrels, and reverse the movement of the syringe plungers to deliver the diluted sample. These operations can be under the push button control of an operator or under computer control. The operator or computer controlled sampling system would hold a sample probe to pick up undiluted sample from a sample receptacle and then transfer the probe to a second receptacle to deliver through the probe both the measured volume of sample and the measured volume of diluent.
One of the important design goals of such automated diluting systems is to deliver diluted samples with accuracy and reproducibility from sample to sample. However, a problem with conventional automated systems is the very fact that they require two syringes, each of which must be actuated by the system control and each of which must automatically be set to a "zero volume" before diluent and sample pick up. The present invention is a method and apparatus for the automated diluting of liquid samples with a single relatively large volume diluent syringe, that is to say, without the use of a second sample syringe. The invention permits diluting operations to occur at rapid sampling rates with high accuracy and reproducibility.